The art of coating a layer of material onto a substrate to achieve certain characteristics in the material, is used in many industries and fields of commerce. One procedure for coating such an article resides essentially in depositing a layer of the desired material across the surface, or part of a surface of the object being coated. Normally the deposited layer is sufficiently thin as to not add substantially to the thickness of the entire surface. However, the coated area will possess characteristics that are essential to the desired function or operation of the object being coated.
As an example of the coating process, in the automotive art certain exhaust gas filters and reactors are provided with a catalytic material or a substance adapted to promote reaction of the exhaust gas. This reaction is followed with the intention of treating the gas prior to its discharge into the atmosphere. Usually for such an article as an exhaust gas filter, the entire unit is dipped or immersed into a bath of coating solution. The unit is then maintained at a desired temperature to best achieve deposition of the coating material.
Generally, in such a process there are a number of factors to be considered for the filter's coating layer to be properly applied and held to the inner surface. Primarily, the coating ingredients must be brought to, and maintained at an optimum concentration and strength. Further, during the coating process, the solution's strength should be maintained by the periodic addition thereto of amounts of the coating elements as the latter leaves the solution to form the coating.
Also, it is desirable to maintain the applied layer at a relatively uniform thickness. This latter requirement, however, becomes difficult in the instance of objects or articles which are of an irregular shape or configuration. Lack of layer uniformity will result for example when the solution does not contact all exposed surfaces for the same period of time.
As is well known, to achieve a proper coating or layer, it is necessary to maintain the coating solution within a preferred temperature range, and to sustain the process over a set period of time.
As mentioned above, a primary defect or fault normally encountered in this type of coating process resides in the shape of the object being coated. Normally, the article is simply dipped into a bath such that it is immersed and consequently all exposed and wetted surfaces in contact with the reacting materials will become coated. Such a process however, could require the removal of excess coating material from certain surfaces that have been exposed to the solution but do not require coating. This latter step of course adds to the overall cost, and the time involved in producing the product.
Other limitations normally embodied in the coating process reside in the capacity of the coating bath to accommodate a limited number of articles. This facet also leads to the problem of irregularity of the coating. Notably, all exposed surfaces will not necessarily be subjected to the same degree of contact time with the solution even though they are completely immersed in the latter.
Toward overcoming these above stated problems as well as to provide a commercially acceptable coating method, the following method is provided. The method herein disclosed is addressed primarily to the coating of irregularly shaped members which normally define an internal filled or unfilled cavity, into which a uniform coating is difficult to apply and for which the coating needs to be restricted to the inside walls of the unit. The term "matrix" as herein used, refers to a bed or mass of a mesh-like material such as steel wool. The function of the latter is to contact the gas for prompt treatment.
Thus, the article, although irregular in shape, and filled with matrix substrate material, is nonetheless adapted to be sealed such that the internal cavity can be made liquid tight. To achieve the in-situ coating, the cavity or cavities will also have previously been provided with separate charges of unmixed solid and liquid components which make up the coating composition. Said components are thereafter mixed, and react to form a coating solution. When said solution is caused to contact the internal cavity walls and matrix, such surfaces will receive a deposit of the coating element.
To achieve the proper degree of such internal coating, each article in sealed condition, can be immersed in a bath or other temperature controlled medium. In the latter, the article is maintained over a period of time, exposed to the solution at a prescribed temperature.
It is therefore an object of the invention to provide a novel method for depositing a uniform coating layer onto an inner substrate surface. A further object is to provide a method for in-situ coating of discrete surfaces of an irregularly shaped article. A still further object is to coat the inner surfaces, including a matrix contained therein, of an exhaust gas manifold or filter.